The present invention relates to a technique for aligning a second projection means to a first projection means.
It may be desirable to align two (or more) cinema projectors in order to obtain the best superimposed projections on the screen. Such alignment is done to increase the level of light on large screens, or for simultaneous “right-eye left-eye” stereoscopic projection in which the images for each eye are assigned to different projectors.
Alignment may also be used to achieve correctly superimposed red, green, and blue images for a given projector. High-end electronic projectors with these three components allow adjusting the superposition (or convergence) of the three primaries by adjusting the orientation of the three imaging systems. Collimation of the three primaries also requires aligning the three primary images projected. This adjustment is not motorized in the present state of the art.
Aligning two projectors is usually a tedious task that requires two people: the projectionist and one other person in the auditorium near the screen. This adjustment is currently manual, and is done as follows: the projectionist projects the same pattern from both projectors, while the person in the auditorium observes the distance between the two projected images on the screen, and uses signals to communicate the correction to be made. The projectionist changes the position of the second projector based on this information (the first one serving as the reference position), until an alignment is obtained that seems satisfactory to the observer. If the projector has a remote control including horizontal and vertical movement of the projected image, the projectionist can then be close to the screen and control the operation manually.
It is even more tedious to adjust the convergence, because the operator works with screws that move the planes of the imaging systems in all three dimensions (rotation and tilt on two axes). The operator must constantly switch between looking at the system alignment screws, which are brightly lit by a lamp, and the screen which is much less brightly lit.